A navigation system performs travel guidance for enabling a user to easily and quickly reach the selected destination. A typical example is a vehicle navigation system where a vehicle is equipped with a navigation function to guide a driver to a destination through a calculated route. Such a navigation system detects the position of the user's vehicle, and reads out map data pertaining to an area at the current vehicle position from a data storage medium, for example, a CD-ROM (compact disc read-only memory), a DVD (digital versatile disc), or a hard disc. Typically, the navigation system displays a map image on a monitor screen on which the current vehicle position and calculated route are illustrated to guide the user to the destination. The user is able to scroll the map image to see desired locations as well.
FIG. 1 shows a display example of a map image on a monitor screen of a navigation system, where the various map elements are shown. This is a typical example of map image showing a downtown area of a city which includes roads, buildings, and POIs (points of interests) that are illustrated in a three-dimensional image. In the example of FIG. 1, it has a large number of POI icons, such as gas stations, restaurants, and hotels as well as many buildings, large scale and small scale roads. Moreover, it also has traffic information icons, function keys and menus bars for operations of the navigation system.
Although the map image presents useful information, the driver would be overwhelmed by vast arrays of information to detect the information which the driver needs at the moment. There may be a danger that the driver can be distracted from driving by overwhelming amount of information, which can lead to a traffic accident. Especially, the important information such as roads and intersections will be hidden by the building images illustrated in the three-dimensional manner as shown in FIG. 1.
Therefore, it is desired that the navigation system is able to prioritize more important information and shows those prioritized information while hiding less important information, thereby assisting the user to concentrate on driving while providing relevant information. Moreover, there is a need of a new display method in that the user can easily switch between a prioritized or simplified map view and a normal map view.